1. Field of the Invention
The invention relates to premium threaded tubular connections comprising at least one set of metal-metal sealing surfaces and makeup abutments on male and female elements that make up the threaded connection, the threaded elements being formed at the end of a tubular component of a great-length pipe or short (coupling) type.
2. Description of the Related Art
Many types of threaded tubular connections are known, primarily used to constitute casing strings or tubing strings or drillpipe strings for hydrocarbon or the like wells, such as geothermal wells.
Threaded tubular connections are also known on riser columns for connecting sea bottom wells to offshore production platforms.
Such threaded tubular connections are subjected to a variety of overall stresses (axial tension or compression, internal or external fluid pressure, bending, torsion), which may be combined (for example axial tension+internal pressure), possibly with fluctuating intensity.
Premium threaded tubular connections not only have to resist rupture but must also remain tightly sealed, in particular to gas, despite such stresses that may be combined and despite tough on-site service conditions.
The stresses may change in nature as the pipes are lowered into the well or during operation; as an example, tensile stresses may briefly change into compressive stresses.
Threaded connections must also be capable of being made up and broken out many times without degradation in performance, in particular by galling.
After breakout, the tubular components can be re-used in other wells under different service conditions.
French patent FR 1 489 013 and European patent EP 0 488 912 describe examples of such premium threaded tubular connections, in particular for a threaded and coupled connection with two great-length pipes joined via a threaded coupling.
U.S. Pat. Nos. 5,687,999 and 4,494,777 describe other examples of an integral premium threaded tubular connection directly connecting two great-length pipes.
The threaded tubular connections described in FR 1 489 013, EP 0 488 912 and U.S. Pat. No. 4,494,777 have a front axial abutment surface at the free end of at least one of the threaded elements, generally the male element, and a sealing surface on a peripheral surface of a threaded element immediately adjacent the front surface of the same threaded element.
The portion of the threaded element between the first thread of the threading and the front axial abutment surface at the free end is generally termed a lip.
In many premium threaded connections and in particular for the last three cited patents, the male sealing surface is located at the end of the male lip, which varies in length depending on the threaded connections.
When a premium threaded tubular connection is made up into the made-up position, the axial abutments are in contact pressure to create a reaction equal to a given makeup torque Tm.
The corresponding male and female sealing surfaces then exhibit radial interference generating a contact pressure and the thread flanks termed “load flanks” located on the thread on the side opposite the free end of the threaded element are in contact under contact pressure, placing the lip under axial compression.
The interfering sealing surfaces can cause problems with galling during make up if they have an unsuitable geometry. They can also run the risk of leaking in service if the contact pressure, and in particular the integrated contact pressure over the active width of the sealing surfaces, is insufficient.
To avoid the risk of leaking, the integrated contact pressure must remain above a certain value expressed in N/mm; for a given geometry, this integrated contact pressure is a function of the relative positioning of the elements at the end of makeup and the service stresses.
It is particularly difficult to obtain a threaded tubular connection that resists, in a manner equivalent to a pipe, the different stresses in service and which remains gas tight under such stresses, the stress after makeup being modified by the application of external stresses in service, for example axial tension or compression, bending, internal or external pressure.